Purification of alkyl phenols



Patented June 8, 1943 romrrca'rron or mm. PHENOLS Daniel B. Luten, Jr., and Aldo De Benedlctis,

' Berkeley, 0

ration of Delaware No Drawing.

alil'., assignors to Shell Development Company, San Francisco,

Calif., a corpo- Application August 27, 1940 Serial No. 354,398

Claims. (01. 260-627) This invention relates to the purification of alkyl phenols by removing nitrogen compounds from them by a solvent extraction process.

The term alkyl phenols, as used herein, refers to mixtures of acid-reacting hydroxy aromatic compounds consisting predominantly of -alkyl phenols, such as may be obtained by extracting cracked mineral oils or coal tar distillates with strong aqueous caustic alkali solutions. These mixtures usually contain nitrogen compounds of a composition not definitely known but apparently comprising lactams, at least a portion of which have slight, if any, basic properties and which cannot therefore be removed by washing the alkyl phenols with acid solutions. 'Nelther can these nitrogen compounds be removed by washing a solution of the phenols in aqueous caustic alkali with a water-immiscible solvent, such as a hydrocarbon liquid. In addition, alkyl phenol mixtures ordinarily also contain small quantities of basic nitrogen compounds which can more or less readily be removedby acid treatment. I

Alkyl phenols have a number of important applications, such as in the flotation of ores, manufacture of resins, cyclic alcohols, ketones and the like; or as anti-oxidants, disinfectants, selective solvents etc. The presence of impurities, such as nitrogen compounds, frequently impairs the usefulness of the alkyl phenols for these purposes.

It is; therefore, the object of this invention to remove from alkyl phenols nitrogen compounds which resist removal by means heretofore known, thereby rendering the former more suitable for the uses to which they are put.

To simplify the language of the specification,

' hereafter nitrogen compounds which are insuiliciently basic to be removed by acid washes are called non-basic" to distinguish them from the nitrogen bases which are removable by scrubbing with acids.

It has now been found that the non-basic nitrogen compounds may be removed by a process in which a basic nitrogen compound is added to the alkyl phenol causing the non-basic nitrogen compounds to become soluble in water so that they may be removed by water washing. It is believed that the non-basic nitrogen compounds form loose complex compounds with alkyl phenols which are water-insoluble, while by themselves the non-basic nitrogen compounds are water-soluble. When pyridine or some other suitable organic'b ase is. added to the system, it reacts with the alkyl phenol to form another,

"more stable, complex, which displaces the nonbaslc compounds from their. complex with the alkyl phenols. 'In this way, the non-basic nitrogen compounds are released andbecome watersoluble so that they may be easily removed by washing with water.

In order to facilitate our treatment, a diluent is ordinarily added to the alkyl phenol mixture to be treated forthe purpose of rendering itless viscous, thus helping phase separation. The diluent used for this'purpose may be any substantially neutral, non-viscous solvent for alkyl phenols which has, a boiling temperature sufliciently different from'the alkyl phenols to enable its separation by fractional distillation, and which does not react with the nitrogen bases nor with the alkyl phenols under the conditions of the treatment. Preferably the diluent comprises one having a preferential solvent power for alkyl phenols, such as ethers of 4-8 carbon atoms, e. g., diethyl ether, diisopropyl ether, dioxan, etc. However, other solvents capable of dissolving the alkyl phenols may be used, such as light hydrocarbon liquids, e. g., light gasoline, pentanes, hexanes, heptanes, octanes, benzene, toluene, xylenes; or oxygenated hydrocarbons, such .as simple alcohols of 3 and more carbon atoms; ketones as acetone, methyl ethyl ketone, methyl propyl ketone, .diethyl ketone, ethyl propyl ketone, etc.; or chlorinated hydrocarbons, such as dichlorethane, chlorpropane, carbon tetrachloride, hexachlorethane and the like. Suitable amounts of diluent may vary from about 25 to 500 volume percent.

In carrying out the present invention, an amount of nitrogen base at least sumcient to displace the non-basic nitrogen compounds from their complexes with the alkyl phenols is admixed with thealkyl phenols or their solution in the diluent. The resulting mixture is then contacted with an amount of water sufficient to form two layers, an alkyl phenol layer containing nitrogen bases, and an aqueous layer containing the nonbasic nitrogen compounds and perhaps a portion of the nitrogen base if the latter is soluble. in water. These layers are then separated.

The amount of nitrogen base used to carry out the treatment may conveniently range from about 50 to 500 mol per cent of the alkyl phenols, and the amount of water should be at least suflicient to dissolve a substantial portion of the relactams.

leased non-basic nitrogen compounds. Ingeneral, the larger the amount of water, the more non-basic nitrogen compounds are removed. Only economical considerations impose an upper limit on these amounts. Thus excessive quantities of water are expensive to handle and may cause losses of alkyl phenols.

The separated alkyl phenol layer may further be contacted with quantities-of nitrogen bases and water under conditions to form two layers which are separated; or else this layer may, if desired, merely be washed with water once or several times to remove as much as possible of the non-basic nitrogen compounds.

In order to reduce possible losses of alkyl phenols by dissolution in the wash water, an inorganic salt, such as sodium chloride, sodium sulfate, calcium chloride, etc., may be dissolved in it in amounts Just suflicient to salt out the alkyl phenols. 7

Any convenient method for effecting the washing may be employed. Thus ordinary mixing and settling in one or several stages may be used; or the liquids may be contacted in a countercurrent column which, if desired, may embody the backwash principle, etc.

A great many nitrogen bases are suitable for accomplishing the described treatment, their main requirement being their ability to displace the non-basic nitrogen compounds from their water-insoluble complexes. Metal hydroxide bases apparently are unable to accomplish this. However, all basic nitrogen compounds which can be dissolved in alkyl phenols or their solutions in a diluent, preferably without forming precipitates, appear to be suitable. In order to facilitate subsequent removal from the alkyl phenol layer, it may be desirable that the nitrogen bases be relatively low boiling. Moreover, it may be advantageous if they are at least partially water-soluble, in that this property facilitates their complete removal from the alkyl phenols with aqueous acid washes.

Examples of suitable bases are pyridine, alkyl pyridines, such as picoline, lutidine, collidine; dipyridyl, halogenated pyridines, nitropyridines, quinoline, .piperazine, piperidine, morpholine, pyrrol, pyrroline, pyrrolidine; ammonia, alkylamines such as methyl amine, ethylamine, propylamine, butylamines, amylamines, hexylamines, cyclohexylamine, dimethylamine, dipropylamine, methyl propylamine, methyl isopropylamine, ethyl propylamine, methyl butylamines, methyl amylamines, trimethylamine, dimethyl ethylamine, dimethyl isopropylamine; aromatic amines as aniline, toluidine; diamines as ethylene diamine, propylene diamine; alkanolamines as ethanolamine, diamino isopropanol; amides, such as formamide, acetamide, urea; petroleum bases obtained by extraction of cracked or straightrun petroleum oils with the aid of dilute mineral acids, etc.

The availability for removal of the non-basic nitrogen compounds seems to depend on their release from a complex with the alkyl phenols by the formation of another more stable complex. The non-basic nitrogen compounds appear to be of the lactam type, and we have found that compounds other than nitrogen bases may also be used to effect this release, provided these other compounds form complexes which are more stable than those formed by ordinary relatively simple Lactams, being amides, are known to formcomplexes with alkyl phenols (seez Kremann and Wenzing Monatshefte fiir Chemie, 38,

480 (1917)). Among the compounds known to form such complexes are the lower fatty acids, particularly those of 1-4 carbon atoms. Indeed, we have found that these fatty acids are capable of extractingconsiderable portions of non-basic nitrogen compounds not removable by strong mineral acids. However, the complexes between the low fatty acids and alkyl phenols are normally not quite as stable as those formed by nitrogen bases with alkyl phenols. Therefore, the fatty acids are for our purpose in general less efficient than nitrogen bases.

The alkali metal salts of the lower fatty acids are also capable of forming complexes with some of the alkyl phenols, and therefore may also be useful in our process.

The. removal of the complex-forming compounds from the purified alkyl phenol layer may be achieved in several ways which depend upon the properties of these compounds themselves. If they are water-soluble, water-washing may remove a considerable portion. Furthermore, distillation,if desired with steam, may be employed in cases where they have relatively low boiling temperatures substantially below the boiling temperatures of the alkyl phenols. If nitrogen bases have been employed, acid washes may be desirable to achieve complete removal of these bases. Thus the alkyl phenol layer may be washed with an aqueous solution of an inorganic acid which is more strongly acidic than the alkyl phenols, such as a dilute sulfuric acid of say 5%-50% concentration, or hydrochloric acid, phosphoric acid, etc. Any suitable combination of these methods may be employed.

Frequently it is advantageous to precede the acid wash with water-washing or distillation or complex-forming compounds may be contami nated. If, for some reason this should be undesirable, the alkyl phenol mixtures may be given a wash with an aqueous solution of a strong mineral acid prior to the treatment of this invention. In this manner, the nitrogen bases naturally associated with the alkyl phenols are pre-rcmoved.

While the nitrogen bases naturally contained in the alkyl phenols help displace the non-basic nitrogen compounds from their complexes, the quantities of the former are normally far too small to have any material effect. Therefore, in many instances the advantages gained by their pre-removal may be greater than any advantage which may result from their presence during the treatment.

Theaqueous layer or layers resulting from the water washes which contain the non-basic nitrogen compounds, and frequently in addition varying amounts of nitrogen bases, as well as alkyl phenols, may be further treated in different ways, depending upon their exact compositions. Frequently, they are merely discarded; or else they may be subjected to fractional distillation, neutralization, acidification, or other conventional means normally employed to separate mixtures of diiferent components having different properties.

The iollowing examples illustrate our invention:

Example 1 An alkyl phenol mixture was obtained by extracting a cracked petroleum distillate with strong caustic soda, steaming the resultant solutlon, and springing it withCOa. A high-boiling fraction of the alkyl phenols so obtained con,- talned 1.85% total and 0.15% basic nitrogen. One liter of this material was dissolved in two liters of diisopropyl ether. The resulting solution was then extracted with one liter of pyridine dissolved in five liters of water. The raiiinate phase obtained was extracted again with one liter of pyridine in five liters of water. The resulting ramnate phase was distilled to remove pyridine and diisopropyl ether, leaving a residue of alkyl phenols amounting to 73.4% of the original charge of alkyl phenols and containing 0.76% total and 0.35% basic nitrogen, of which a considerable portion was pyridine. Upon fractionally distilling this material to produce three fractions, two end fractions of about each or less and a middle fraction of at least 80%, it is round that the middle fraction contains less than .l% nitrogen.

The extract phase was extracted with diisopropyl ether to remove the small amounts of dissolved phenols, and was then distilled to remove the pyridine (as its constant boiling mixture with water) and water. The lactams which were left as a residue by this treatment were vacuum distilled, giving a product amounting to 15% of the alkyl phenols charged and containing 10.8% nitrogen.

Example 2 One volume of a coal tar cresylic acid obtained from a commercial sample of high-boiling tar acid and containing 1.20% total and 0.28% basic nitrogen was dissolved in two volumes of diisopropyl ether and extracted with one volume of pyridine and five volumes of water. The rafiinate phase was washed with sulphuric acid and the diisopropyl ether removed by distillation. The alkyl phenols recovered amounted to 89.3% of the charge and contained 0.08% total and no basic nitrogen.

Example 3 One liter of high-boiling petroleum cresylic acid containing 1.85% total and 0.15% basic nitrogen was dissolved in two liters of diisopropyl etherand extracted -first with five liters of 2.7% aqueous ammonia, then with five liters of water and, finally, withone liter of 25% sul phuric acid. The diisopropyl ether was'distilled from the rafinate phase and the residual alkyl phenols vacuum distilled. The total alkyl phenols recovered, including vacuum distillation bottoms, amounted to 82.2% of the charged alkyl phenols. The nitrogen content of the vacuum distilled phenols was 0.50%.

Example 4 One volume oi a high-boiling petroleum cresylic acid containing 2.38% nitrogen was dissolved in two volumes of hexane and extracted with one volume ofv pyridine dissolved in five volumes of water. The raifinate was extracted with another five-volume portion-oi. water and, finally, with 1.5 volumes of 25% sulphuric acid. The hexane was distilled from the rafllnate phase, leaving a residue 01 alkyl pheno which amount to 80% of the charged alkyl phenols and contained 0.85%

nitrogen.

- able from said 2. The process of claim 1 wherein the nitrogen base is at least partialb' water-soluble;

8. The process or claim 1 wherein the nitrogen base has a boiling temperature lower than the boiling temperatures or the alkyl phenols.

4. The process or claim 1 wherein the amount of said nitrogen base is from 50 to 500 molpercent of the alkyl phenols.

5. The process or claim 1 wherein the nitrogen base is an organic nitrogen base.

6. The process of claim 1 wherein base is a pyridine base.

'7. The process or claim 1 wherein the nitrogen baseispyridine.

8. The process of claim base is ammonia.

9. The process of claim 1 wherein the wash water contains an inorganic salt to salt out dissolved alkyl Phenols.

10. In the process of purifying alkyl phenols containing non-basic nitrogen compounds naturallyassociated with petroleum and coal tar alkyl phenols, which compounds are not removable irom said alkyl phenols by strong mineral acid washes, the steps comprising dissolving in said alkyl phenols at least 50 mol percent of a nitrogen base, and then washing the resulting solution with an aqueous solution of a strong mineral acid.

11. In the process of purifying alkyl phenols containing non-basic nitrogen compounds naturally associated with petroleum and coal tar allqrl phenols, which compounds are not remov- 1 wherein the nitrogen acid washes, the. steps comprising dissolving in said alkyl phenols at least 50 mol percent of a nitrogen base, and then washing the resultin solution with water and an aqueous solution or a strong mineral acid.

12. In the process of purifying alkyl phenols containing non-basic nitrogen compounds naturally associated with petroleum and coal tar alkyl phenols, which compounds are not removable from said alkyl phenols by strong mineral acid washes, the steps comprising washing said alkyl phenols with water in the presence of a nitrogen base dissolved in said alkyl phenols,

said base being present in an amount at least 50 moi percent of said alkyl phenols, whereby two layers are formed, an alkyl phenol layer containing at least a substantial portion of said nitrogen base, and an aqueous layer containing at least a portion otsaid non-basic nitrogen compounds, separating the layers and removing the nitrogen base from the alkyl phenol layer.

13. In the process ,of purifying alkyl phenols containing non-basic nitrogen compounds naturally associated with petroleum and coal tar alkyl phenols, which compounds are not removable from said alkyl phenols by strong mineral acid washes, the improvement comprising wash- 7 ing said alkyl phenols with water in the presence of a neutral solvent for said alkyl phenols, inert under the conditions of the'process, and of a nitrogen base dissolved in said alkyl phenols, said the nitrogen alkyl phenols by strong mineral layers are formed, an alkyl phenol layer containlng at least a substantial portion of said nitrogen base and said solvent, and an aqueous layer containing at least a. portion 01' said non-basic nitrogen compounds, separating the layers, and removing said dissolved nitrogen base and solvent from the alkyl phenol layer.

14. The process of is an ether.

claim 13 wherein the solvent 7 15. The process of claim 13 wherein the amount from 25 to 50% by volume of of said solvent is 5 said alkyl Phenols DANIEL B. LUTEN, JR. ALDO DE BENEDICTIS. 

